Method for making films utilizing a pulsed laser for ion injection and deposition

ABSTRACT

A tapered profile magnetic field pulsed laser deposition (PLD) system and method for depositing a thin film on a substrate are provided. The system includes a tapered pulsed coil arranged relative to a confinement magnetic device so that the plume discharged from the confinement magnetic device is collected and concentrated by an inwardly tapered surface of the tapered pulsed coil which causes the plume to be deflected towards a substrate on which the charged species are deposited to form the thin film. In yet a further aspect, a device for maintaining cleanliness of an interior of a deposition chamber laser entry window through which a laser beam enters and converges to a target is provided. A plume that is generated when a laser beam ablates the target is ionized as a result of radioactive members such that the ionized plume is deflected toward one of the first members (e.g., metal plates) as opposed to coating the interior of the laser entry window.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/051,211 filed Jan. 16, 2002 which claims the benefit of U.S.Patent Application Ser. No. 60/262,051, filed Jan. 17, 2001, all ofwhich are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to processes for forming thinfilms and more specifically, relates to pulsed laser deposition methodsusing a desired target material for forming high quality thin films on asubstrate.

BACKGROUND

Over the years, a number of different techniques have been developedand/or proposed for forming thin films on a substrate. As more and moreapplications for thin films are contemplated and new types of materialsare discovered, there is a continuing need to produce high qualityfilms. For example, the discovery of high T_(c) superconductor materialsprecipitated a great deal of research into the development of apractical method for making such materials. The primary practicalapplication for such materials is the formation of thin films which maybe used in certain instruments, such as SQUIDS and bolometers. Thinfilms formed of these materials may also be used for the generalfabrication of superconductors in the form of thin films deposited ontowires or tapes. This is only one type of thin film application whichrequires a fabrication method which offers the precision and highquality necessary to produce such films.

Pulsed laser deposition (PLD) is a versatile deposition technique thathas been in use for several years. The technique is based upon thevaporization of a small region of a target material by a high powerlaser. The technique has particular application in the deposition ofoxide films, such as high temperature superconductors, ferrites, andceramic films. The target material is then subsequently collected on asubstrate in the form of a film deposited onto the substrate surface.Typically, the technique employs a series of very short (nanosecondduration) pulses, principally from a laser source which ablates thesurface of the target material and then by using various means, thetarget material is deposited as a thin film on the substrate. The PLDmethod offers many advantages over other types of techniques for forminga thin film on a substrate. For example, the PLD method offers ease ofdeposition and the formation of crystalline films with good adhesion atlow temperatures, even as low as room temperature. Another advantage ofthe PLD technique is the ability to reproduce the stoichiometry of thetarget in the film, including that of the multi-component targets. PLDis desirable for routine deposition at room or higher temperaturesproviding high quality crystalline thin films.

PLD is an excellent method for use in superconductor film growthprocesses and other coating processes for forming high quality thinfilms. PLD involves laser ablation and evaporation of a target materialby a high power laser. The ablated material forms a plume comprisingboth undesirable large particles and desirable atoms and ions which allget deposited on a substrate. More specifically, the plume includesions, electrons, atom clusters, and larger particulates of varyingsizes. The plume extends from the target in a direction outward from thetarget. Often, the substrate is positioned so that it is directly infront of the target, at a distance of a few inches. Thus, the plumespreads onto the substrate to form the thin film. In this arrangement,the direct plume has a range of atom clusters and particulate sizes. Thesubstrate may also be placed alongside the plume to collect a greaterpercentage of atomic species but at a lower deposition rate.

One of the disadvantages of using the PLD technique is that undesirableparticulates form a part of the plume and are directed onto thesubstrate. These particulates generally constitute the large particleswhich are present in the plume and have sizes on the order of betweenabout 0.1 to about 5.0 μm in size. The inclusion of this size ofparticles in the thin film disadvantageously limits PLDcommercialization. Most of the conventional PLD methodsdisadvantageously produce a particle density of about 400 particles percm².

The laser ablation of the target material also results in the creationof charged and neutral species having a varying degree of sizes. Onlyspecies of atomic dimensions of the target material are desired to bedeposited on the substrate to form the thin film. If larger sizedparticulates form on the substrate, these particulates limit theuniformity of the deposited thin films and its applications. Theseparticulates are formed as a result of a number of factors relative tothe target. More specifically, the target may include a protrudingsurface; the target may have micro-cracks that are mechanicallydislodged due to laser induced thermal or mechanical shock during thelaser ablation process. In addition, larger particulates may be formedas a result of rapid expulsion of trapped gas bubbles beneath the targetsurface during laser irradiation and also the splashing of molten layersof the target material may result in the formation of largerparticulates.

The presence of larger particulates in the thin film has seriousramifications in some specialized applications, such as tribologicalapplications. In these type of applications, it is desirable to depositcoatings with very high hardness on precision bearings. These hardcoatings can protect the steel surfaces of the bearings from wear andthereby improve the lifetime of the bearings. By increasing the lifetimeof the bearings, the performance of a variety of moving mechanicalassemblies can be improved. For example, machinery and pump performancecan be improved due to this improved wear. PLD is an excellent techniquefor depositing such hard coatings; however, the incorporation of larger,hard particulate material in the coatings negatively impacts theperformance of the bearings as these materials often have abrasive-likeproperties. The presence of abrasive-like particles in the coating canact to deteriorate and destroy the coating. This results in theproduction of more debris and also to a loss of coating adhesion.

Another limitation of the PLD method is that it is difficult to scale upthe deposition process to accommodate larger size substrates having asurface area of about 10 cm². To grow large area uniform films requiresthat the substrates be moved to accommodate uniform deposition over alarger area than the physical plume size.

Accordingly, the predominant problem with PLD methods is the creationand deposition of large particulates that impose a limitation on thepotential scope of applications for the PLD method. These and otherdisadvantages or problems are solved or reduced using the apparatus andmethod of the present invention.

SUMMARY

According to the present invention, a method for forming high qualitythin films using a pulsed laser deposition (PLD) system is provided. Inone exemplary embodiment, the system includes a PLD chamber wherein alaser beam ablates a target material creating an ionized plasma plume ofions and electrons which is diverted and deposited onto a substrateusing a confinement magnet followed sequentially by a deflection magnet.

More specifically, the ablation of the target creates a plume of atomicspecies atoms, ions, electrons, atomic clusters, and particulates ofvarying sizes. The target is disposed in close proximity to theconfinement magnet so that the plume is directed into the confinementmagnet. The confinement magnet generates a magnetic field parallel tothe plume ejection direction from the laser target. This magnetic fieldcounters the tendency for the plume to naturally diverge and thereforeacts to focus and concentrate the plume as it travels away from thetarget.

The concentrated plume is then introduced into the deflection magnetwhich includes magnetic coils and serves to apply a magnetic field todeflect the electrons and accompanying ions to the substrate. In oneembodiment, the deflection magnet is a tubular magnetic member having anopening extending therethrough for receiving the plume. The deflectionmagnet generates an axial magnetic field which is parallel to the laserplume ejection direction (similar to the confinement magnet). Thedeflection magnet has a bend formed therein at an end proximate to thesubstrate for directing the plume onto the substrate which is disposedaway from a longitudinal axis extending through the target and theconfinement magnet. The magnetic field generated in the deflectionmagnet, including the bent portion thereof, constitutes a mechanism forfiltering the neutral, uncharged matter (e.g., the atomic clusters andthe particulates) of the plume from the charged matter (the atomicspecies atoms and the ions). The uncharged matter is not influenced bythe magnetic field and thus travels in a relatively linear trajectoryfrom the target through the confinement and deflection magnets. In thismanner, only the charged matter is deflected onto the substrate to formthe thin film and the undesirable atomic clusters and particulates arenot deflected onto the substrate.

In another aspect of the present invention, deflector plates aredisposed within the deflection magnet and an electric field is generatedacross the plates. A negatively charged plate acts to repel negativeelectrons away from the outer curved wall of the deflection magnet andtoward a positively charged plate on an opposite surface of thedeflection magnet. Because the positive ions are attracted to thenegative electrons, the ions are thus assisted, especially in the bentportion, in following the electrons along the magnetic field directionof the deflection magnet toward the substrate.

Accordingly, the present invention, provides a simple, relativelyinexpensive, yet effective PLD method of forming extremely clean filmswith reduced particulate densities and size. This method favors usefulfilm properties, such as crystallinity and good adhesion, event at roomtemperature, because it relies upon using high energy ions for thedeposition. The method therefore has tremendous potential forapplications where the substrate is thermally sensitive. The presentmethod may be applied to the production of a film from a great number ofmaterials.

In yet another aspect, a tapered profile magnetic field pulsed laserdeposition (PLD) system and method for depositing a thin film on asubstrate are provided. The system includes a platform for holding atarget; a laser source producing a laser beam that is focused on thetarget to form a plume having charged species and neutral species; aswell as a confinement magnetic device disposed proximate to the targetsuch that the plume is influenced by a first magnetic field generated bythe confinement magnetic device. The first magnetic field causes theplume to become more focused and is substantially parallel to a plumeejection direction of the plume as it travels away from the target. Thesystem also includes a tapered pulsed coil arranged relative to theconfinement magnetic device so that the focused plume discharged fromthe confinement magnetic device is collected and concentrated by aninwardly tapered surface of the tapered pulsed coil which causes theplume to be deflected towards a substrate on which the charged speciesare deposited to form the thin film.

In yet a further aspect, a device for maintaining cleanliness of aninterior of a deposition chamber laser entry window through which alaser beam enters and converges to a target is provided. The deviceincludes a pair of first members disposed between the laser entry windowand the target with a space formed therebetween. A pair of radioactivemembers are disposed in the space between the pair of first members andthe first members are operatively connected to a voltage source andground so that a voltage potential difference is created therebetween.The converging laser beam enters the space between the first members atone end thereof and travel therebetween in a converging manner towardthe target. A plume that is generated when the laser beam ablates thetarget is ionized as a result of the radioactive members such that theionized plume is deflected toward one of the first members as opposed tocoating the interior of the laser entry window.

Other features and advantages of the present invention will be apparentfrom the following detailed description when read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will be morereadily apparent from the following detailed description and drawings ofillustrative embodiments of the invention in which:

FIG. 1 is a side perspective of a magnetic field pulsed laser depositionsystem according to a first embodiment;

FIG. 2 is a partial perspective cross-sectional side elevational view ofa magnetic field pulsed laser deposition system according to a secondembodiment;

FIG. 3 is a top plan view, shown in partial cross-section, of thedeposition system of FIG. 2;

FIGS. 4a and 4 b illustrate two circuits for generating current tosupply a magnetic field in the deposition system according to oneexemplary embodiment;

FIG. 5 shows the collector current for the second embodiment of thepresent invention as a function of the deflection tube magnetic fieldlevel and deflection plate bias level;

FIG. 6 is a cross-sectional view of a magnetic field pulsed laserdeposition system according to a third embodiment;

FIG. 7 is a cross-sectional view of a magnetic field pulsed laserdeposition system according to a fourth embodiment;

FIG. 8 is a cross-sectional view of a magnetic field pulsed laserdeposition system according to a fifth embodiment;

FIG. 9 is a cross-sectional view of a magnetic field pulsed laserdeposition system according to a sixth embodiment;

FIG. 10 is a cross-sectional view of an ion assisted pulsed laserdeposition system according to a seventh embodiment; and

FIG. 11 is a cross-sectional view of a device for keeping clean theinside of a deposition chamber laser entry window.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 and in accordance with the present invention, amagnetic field pulsed laser deposition (PLD) system for obtaining highlyuniform and smooth films with the PLD process is generally shown at 10.An excimer laser 20 operating with a selected gas or gas mixture andhaving a predetermined wavelength along with a pulse width is used toprovide a laser beam. For example, the laser 20 may operate with amixture of Ne, Kr and F gases. The laser light preferably has anultraviolet wavelength of about 248 nm. One suitable laser 20 is aLambda Physik excimer laser Model LPX 305Fi which operates with anenergy per pulse of about 1000 to about 1300 mJ at a repetitionfrequency of about 10 to about 50 Hz. The laser pulse duration istypically about 10 to about 30 ns and more preferably from about 10 toabout 15 ns.

The laser beam is focused on a target 30 of choice which is typicallyheld in a target holder (not shown). The target 30 is formed of anynumber of types of solid materials which are laser ablatable. The targetis selected in view of the type of thin film the user desires to produceusing the PLD method. For example, the target 30 may be formed of oneelement or may be formed of several elements. The target 30 may beformed of titanium, aluminum, aluminum nitride, titanium nitride,carbon, cobalt compounds, such as samarium cobalt and iron cobalt, andcarbide compounds, such as titanium carbide. The target 30 is preferablyplaced in the target holder and is rotated at a selected speed, i.e.,10-100 rpm, during the PLD method. The target 30 may also be oscillatedduring the process so that the laser beam erodes a circular region ofthe target 30.

The system 10 also includes a substrate 40 on which the thin film isformed from the ablation of the target material 30. The substrate 40 canbe any solid material which is appropriate because of its mechanical,optical, electronic, or chemical properties. A reactive gas may beintroduced into the system so that it reacts with a plasma plume 31created when the target 30 is vaporized forming a new material which isionized and directed toward the substrate 40 for deposition of the thinfilm thereon. For example, a low pressure gas, such as oxygen ornitrogen can be used to accomplish reactive deposition for thedeposition of oxides and nitrides respectively. For example a TiC targetand nitrogen reactive gas may produce ionized TiCN which is thendirected to the substrate 40. In another example, methane gas (CH₄) witha Ti target 30 can be used to deposit TiC films. Similar to the targetholder, the substrate 40 may be disposed in a substrate holder (notshown) which also may be caused to rotate to produce a more uniformfilm. It is also within the scope of the present invention that thesubstrate 40 may be heated to an elevated temperature or maintained atroom temperature and furthermore, the substrate 40 may be electricallybiased to improve the rate of film growth. In the exemplary embodiment,a target of a material is used to deposit a film of the same material.

When the laser 20 is activated, pulsed energy is directed to a region ofthe target 30 to form the plume 31 of vaporized target materialcontaining ions, electrons, larger atom clusters, and particulates. Inaccordance with the present invention, the atomic species atoms and theions are then collected onto the substrate 40 while the atomic clustersand particulates remain largely in line of sight trajectories and arediscriminated against so that they are not deposited onto the substrate40. The pulsed laser ejection plume 31 is used as an ion source forsubsequent deflection and collection. The deposited film then resultsfrom the impingement of uniformly atomic species.

The system 10 also includes a confinement magnet 50 and a deflectionmagnet 60. The confinement magnet 50 is a permanent magnet having anopening 52 extending therethrough from one end 53 to another end 54. Theexemplary confinement magnet 50 thus is a ring-like member which is usedto produce a magnetic field parallel to the plume ejection direction infront of the laser target 30. The target 30 is arranged relative to theconfinement magnet 50 so that the formed plume 31 is directed into theopening extending axially through the confinement magnet 50. Themagnetic forces of the magnet 50 counters the natural divergence of theplume 31 and acts to focus the plume 31 within this area as it isdirected toward the substrate 40 and away from the target 30.

The confinement magnet 50 is also designed to focus the electrons andbecause of the magnetic field applied by the confinement magnet 50, theelectrons follow a spiral or helical path along the magnetic field asthe electrons travel through the confinement magnet 50. The confinementmagnet 50 generates higher ion density within the plume 31 as themagnetic field causes the electrons to ionize surrounding neutral atoms.This is the case because as the electrons travel in the helical path,the probability that the electrons will collide with neutral atomsincreases. As this occurs, an increased ion density results and the ionsare “dragged” along with the electrons to the substrate 40.

In the first embodiment shown in FIG. 1, the deflection magnet 60 isformed of magnetic field coils which apply a magnetic field to deflectthe electrons and accompanying ions to the substrate 40 placed away fromthe direct line of sight from the target 30. The deflection magnet 60may be formed of a series of spaced magnetic coils such that the magnet60 has a section which is angled (bent) so that the plume 31 is directedonto the substrate 40 (which is disposed away from the direct line ofsight of the target 30). The deflection magnet 60 is angled at one end63 so that it directs the contained plume 31 to the substrate 40. In theexemplary embodiment, the end region 63 of the deflection magnet 60opposite the end region 61 (which faces the confinement magnet 50) isangled relative to the end region 61. In the illustrated embodiment, thedeflection magnet 60 has about a 45° angled end region 63.

The deflection magnet 60 is preferably an annular member and morespecifically has an opening extending axially therethrough from endregion 61 to end region 63. The deflection magnet 60 may therefore beformed of a unitary member having a series of magnetic coils or it maybe formed of a series of separate magnetic coils which are spaced apartfrom one another. In the case of the latter, the magnet 60 may be easilybent to incorporate the desired angle into the magnet 60 so as toproperly direct the plume 31 onto the substrate 40. The opening receivesthe concentrated plume 31 as it exits the confinement magnet 50 and themagnetic field applied by the coils influences the direction of travelof the charged matter. Therefore, the bending of the deflection magnet60 permits the travel direction of the charged matter to be controlledand directed toward the substrate 40. The general direction in which thecharged matter travels is indicated by arrows 19.

Because the atomic clusters and the particulates are not charged, theyare not influenced by the magnetic field and therefore will travel in anaxial direction which is generally parallel to the longitudinal axis ofthe confinement magnet 50. The uncharged matter will therefore not bedeflected to the substrate 40 but rather will proceed in a “line ofsight” trajectory relative to the target 30. This advantageously resultsin the atomic clusters and particulates not being deposited onto thesubstrate 40. Conversely, the charged matter, i.e., the electrons andaccompanying ions, is influenced by the magnetic field and is deflectedto the substrate 40.

Accordingly, the present invention provides an apparatus and method ofcollecting the atomic species atoms and the ions onto the substrate 40to form a thin film, while the atomic clusters and particulates remainlargely in line of sight trajectories and are discriminated against. Inaddition, the pulsed laser ejection plume 31 is used as an ion sourcefor subsequent deflection and collection. Since the deflection mechanismacts upon the electrons and the ions are dragged along, multi-elementtargets 30 can be utilized as well as single element targets 30.

In another aspect of the present invention, the deflection magnet 60 mayinclude one or more baffle members or a roughened internal surface (notshown), both of which are designed to capture large atomic clusters andparticulates as the plume 31 travels through the deflection magnet 60.In other words, by modifying the internal surface structure of thedeflection magnet 60, a mechanism is created to capture and retain thelarger undesirable matter, i.e., atomic clusters and particulates. Thismatter becomes lodged within the modified internal surface due to itssize and construction and thus, its forward progress is inhibited.

Now referring to FIGS. 2-5, a magnetic field pulsed laser depositionsystem according to a second embodiment of the present invention isgenerally indicated at 100. The system 100 includes the target 30, thesubstrate 40 and a confinement magnet 110. The confinement magnet 110actually is formed of a pair of permanent magnets 112, 114 which areused to produce a magnetic field parallel to the plume ejectiondirection in front of the laser target 30. Each of the magnets 112, 114has a north (N) pole 116 and a south (S) pole 118. Magnets 112, 114 arearranged so that the N pole 116 of the magnet 112 opposes the N pole 116of the magnet 114 and the S pole 118 of the magnet 112 opposes the Spole 118 of the magnet 114. The like magnetic poles 116, 118 oppose eachother so that the magnetic field from each of the magnets 112, 114 loopsfrom the N magnetic pole 116 to the S magnetic pole 118 of each ofmagnets 112, 114 creating a magnetic field that is substantiallyparallel to the plume direction. This parallel magnetic field preventsthe plume 31 from further converging and actually causes the plume 31 tobecome refocused into a narrow plume 31 as it travels through theconfinement magnet 110.

In one embodiment, the confinement magnet 110 generates a magnetic fieldthat has an amplitude of about 45 mT (milli-Tesla) parallel to the plume31 direction. In this manner, a relatively strong magnetic field can becreated without introducing a joule heating that would accompany amagnetic field generated by introducing a current in a resistivesolenoid. As can be seen from FIG. 2, a gap 117 is formed between themagnets 112, 114 and the laser 20 may be positioned so that the laserbeam is directed through this gap 117 onto the target 30. The target 30is disposed a predetermined distance from one end 115 of the magnets112, 114. The distance the target 30 should be placed from the magnets112, 114 depends upon several factors, including but not limited to thetype of material forming the target 30. In any event, the target 30 andthe magnets 112, 114 should be placed at a distance where substantiallyall of the plume 31 will be directed into the gap 117. In oneembodiment, the target 30 is placed at a distance of from about 1 cm toabout 4 cm and preferably from about 1 cm to about 2 cm. It will beappreciated that these distances are merely exemplary in nature andother distances may be used. As best show in FIG. 2, the central regionof the target 30 at which the laser beam is directed should be axiallyaligned with the gap 117 so that the plume 31 travels into the gap 117.Thus, one of the advantages of this configuration is that the laser 20has free access to the target 30 from one of two sides. Furthermore, thetarget 30 is conveniently located so that it may be freely and easilyreplaced. One type of target 30 is a cylindrical laser target having adiameter of about 25 mm and a thickness of about 6 mm.

The system 100 also includes a deflection magnet 130 which is used togenerate an axial magnetic field in a direction parallel to the laserplume ejection direction, similar to the confinement magnet 110. Thedeflection magnet 130 has a first deflection section 131 and a seconddeflection section 133. The deflection magnet 130 is preferably in theshape of a tubular magnetic member and includes a first end 132 and anopposing second end 134 with the first end 132 being spaced from andfacing the confinement magnet 110. The second end 134 is positionedproximate to the substrate 40 so that the charged matter is directed outof the second end 134 and onto the substrate 40 to form the thin film.As best shown in FIG. 2, in one exemplary embodiment, each of the firstand second deflection sections 131, 133 is a semicircular magnetic coresurface with an opening 136 being formed between the opposing first andsecond deflection sections 131, 133, as best shown in the top plan viewof FIG. 3. The opening 136 extends axially along a longitudinaldirection of the sections 131, 133. In one exemplary embodiment, thedeflection magnet 130 is solenoid coil formed of suitable magneticmaterial. In other words, the deflection magnet 130 is a member whichcontains the plume 31 and directs it to the substrate 40. According toone exemplary embodiment, the deflection magnet 130 is a solenoid coilwound from #18 gauge copper magnet wire which is used to generate anaxial magnetic field along the length of the deflection magnet 130 andin the same direction as the axial magnetic field generated by themagnets 112, 114. Thus, both the confinement magnet 110 and thedeflection magnet 130 generate axial magnetic fields. It will beappreciated that any number of other magnetic members may be used solong as the member generates an axial magnetic field along the length ofthe deflection magnet 130.

Further, because the deflection magnet 130 is a tubular member, theopening 136 has a generally annular shape and has a selected diameterwhich is sufficient to receive substantially all of the plume 31 afterit is formed and travels through the confinement magnet 110. Thus, thereis a relationship between the size of the gap 117 and the diameter ofthe opening 136 since the diameter of the opening 136 should be ofsimilar size as the gap 117 so that the focused plume 31 exiting the gap117 properly enters the opening 136. In one exemplary embodiment, thediameter of the opening 136 is about 3.5 cm.

As best shown in FIG. 3, the deflection magnet 130 has a bendincorporated along a portion of its length. More specifically, thesecond end 134 is bent relative to the first end 132 so that the plume31 enters the deflection magnet 130 along one axial direction and exitsthe deflection magnet 130 along another axial direction. An angle isformed between these axises and in one exemplary embodiment, the angleis about 45°. In other words, a 45° bend is incorporated into thedeflection magnet 130 so that selected components of the plume 31 exitthe deflection magnet 130 at about a 45° angle relative to the axiscontaining the plume 31 as it enters the deflection magnet 130 and thetarget 30. The substrate 40 is positioned so that it faces the opening136 at the second end 134.

The system 100 also includes first and second deflector plates 140, 142which are disposed within the opening 136 of the deflection magnet 130so that they extend along an axial length of the deflection magnet 130.The first and second plates 140,142 are formed of a conductive materialand are preferably in the form of metal strips. In one exemplaryembodiment, the first and second plates 140, 142 have a width of about1.5 cm. The first and second plates 140, 142 may have other widths witha maximum width being slightly less than ½ the radius of the opening136. The first and second plates 140, 142 are arranged along oppositesides of the deflection magnet 130 within the opening 136 so that onesurface of one of the plates 140, 142 faces the other. The plates 140,142 may have any number of shapes and in the exemplary embodiment, theplates 140, 142 are generally rectangular shaped. The first plate 140 isalso referred to as an outer plate and the second plate 142 is referredto as an inner plate. Because of the bend in the deflection magnet 130,the first plate 140 is disposed on an outer curvature portion (firstsection 131) of the magnet 130 which has a greater axial length from end132 to end 134 while the second plate 142 is disposed on an innercurvature portion (second section 133) of the magnet 130 and thereforehas a lesser axial length from end 132 to end 134.

Preferably, the first and second plates 140, 142 are insulated from thedeflection magnet 130 using known techniques. For example, a glasssubstrate (not shown) may be disposed between each of the plates 140,142 and the respective section of the deflection magnet 130. Accordingto the present invention, a negative voltage is applied to the firstplate 140 relative to the second plate 142. The voltage is applied tothe plates 140, 142 using known techniques, including the use of one ormore external or internal power supplies. By applying respectivevoltages to the plates 140, 142, an electric field is generated and isdirected across the inner tube diameter (across the opening 136). Morespecifically, the electric field is directed from the second plate 142toward the first plate 140 across the opening 136.

The operation of the system 100 will now be described. As with thesystem 10, the laser 20 is actuated and a laser beam is directed uponthe target 30 to produce the plume 31. The plume 31 then enters the gap117 between the magnets 112, 114. The magnetic field generated by themagnets 112, 114, in a direction parallel to the plume ejectiondirection, causes the diverging plume 31 to converge and become morefocused as it travels within the gap 117 between the magnets 112, 114.Furthermore and as previously-mentioned, the magnetic field causes theelectrons to travel in a generally helical-like path and causesincreased ionization of the plume 31 as electrons strike neutral atoms.All of the constituents of the plume 31 exit the magnetic fieldgenerated by the magnets 112, 114 and then enter the opening 136 at thefirst end 132 of the deflection magnet 130.

The axial magnetic field generated by the deflection magnet 130influences the charged components of the plume 31 and by incorporating abend into the deflection magnet 130, the charged components aredeflected, while the neutral components are not deflected. The magneticfield also acts on the charged components and therefore, the presentinvention uses the applied magnetic field and the configuration of thedeflection magnet 130 to filter and deflect the desired chargedcomponents, while the neutral components simply travel along the initialejection direction. In one exemplary embodiment, the deflection magnet130 generates magnetic field levels that are strong enough to magnetizethe electrons and cause them to spiral along the magnetic field lineswith a helical radius that is less than that of the inner tube diameter(the diameter of opening 136). The magnetic field levels are not strongenough to appreciably deflect the ions over the length of the coillength. For example, the magnetic field levels may be between about 10mT and about 100 mT. Because of the electrostatic attraction between theelectrons and the ions, the ions are caused to deflect in response tothe deflection of the electrons (so called “dragging of the ions” by theelectrons).

The result is that the electrons and ions are deflected due to themagnetic field, while the atom clusters and the particulates are notdeflected. As best shown in FIG. 3, the plume 31 enters the opening 136generally having a first axial direction. This first axial directionextends through the gap 117 and is generally perpendicular to the target30. Because the first and second sections 131, 133 have bends, theopening 136 does not define a linear path but rather defines a curvedpath. Accordingly, any constituent of the plume 31 which travels alongthe first axial direction will impact and strike one of the walls of thesections 131, 133. More specifically and as shown in FIG. 3, the firstaxis intersects the section 131 (outer curvature of the deflectionmagnet 130) and therefore any component traveling along the first axisimpacts the section 131.

Because the second plate 142 is positively charged and an electric fieldis directed across the opening 136 toward the first plate 140, thenegative electrons are repelled from the outer curvature (section 131 ofthe deflection magnet 130) because of their like charge. The first plate140 thus assists in keeping the electrons away from the outer curvatureof the magnet 130 and instead, the positive ions are dragged with theelectrons and are directed toward the center region of the opening 136and toward the second plate 142. The ions are thus assisted to followthe electrons along the magnetic field direction toward the substrate 40where the thin film is formed. Accordingly, one of skill in the art willappreciate that by providing the arrangement shown in FIGS. 2 and 3, thedesired components of the plume 31 are effectively delivered to thesubstrate 40, while the undesirable components, i.e., the atomicclusters and particulates are not directed to the substrate 40 and thusdo not adversely impact the formation of the thin film.

According to the present invention, any number of methods of poweringthe magnet coil (magnets 130) may be used. Two exemplary methods of thepowering the deflection magnet 130 are illustrated in the circuitdiagrams of FIGS. 4a and 4 b. In one embodiment, a direct current (DC)is used to generate a steady magnetic field in the coil (deflectionmagnet 130) for causing the deflection of the discharge plasma generatedby the laser pulse through an angle of about 45°. This embodiment isgenerally illustrated in FIG. 4a. A circuit 160 is shown for generatingthe current to supply the magnetic field in the coil which is denoted byits inductance 162. In the first embodiment, a straight continuouscurrent is generated in the coils and the circuit 160 is defined by avoltage source 164 connected in series to the coil (inductance 162) withthe magnetic coil having a resistance, generally indicated at 166.

In the exemplary magnet coil (deflection magnet 130), it is preferred togenerate a magnetic field of about 4 mT per ampere. A DC current ofabout 4 A is required to generate an axial magnetic field of about 16mT. The magnet coil has a resistance of about 4 ohm. Consequently, for amagnet current of 2 A, the power dissipated is 16 watts, and at 4 A only64 watts is dissipated. This heating is far less than in designs thathave all the magnetic fields generated by electromagnets.

A second method for generating the current to supply the magnetic fieldin the deflection magnet coil is illustrated in FIG. 4b. In this secondmethod, the time over which the magnetic field is present can berestricted to the time in which the guided plasma discharge is present.This can reduce the duty cycle of the deflection coil and lower the heatload on the system 100. This second method is illustrated by a circuit170 which is designed so that the trigger pulse used to generate thelaser pulse is also used to close a switch 172 which connects the coil,denoted by inductance 174, across a capacitor 176. The circuit 170 has afirst resistor 178 and a second resistor 180 with the first resistor 178being in series with a voltage source 182 and the capacitor 176. Thesecond resistor 180 is in series with the switch 172 and the coil(inductance 174). The first resistor 178 has a value which issignificantly less than the value of the second resistor 180. A timedelay 190 is incorporated into a laser trigger pulse circuit, generallyindicated at 192, so that the magnetic field in the coil reaches itsmaximum value before the laser 20 (FIG. 1) is fired. In other words,once the switch 172 closes, current flows to the coil and causes thegeneration of the magnetic field. The time delay 190 prevents the laser20 from immediately firing an energy pulse upon the closing of theswitch 172, but rather the energy pulse is fired after a predeterminedamount of time has passed. This delay ensures that the plume 31 iseffectively deflected because the magnetic field has time to reach anoptimum strength.

To illustrate the effectiveness of the system 100, the normal substratehas been replaced by a metal disk having an area of about 1 cm². Thisprobe disk has an area that is much less than that of the deflector tubeinner cross sectional area and is located 1.5 cm beyond the deflectionmagnet 130 along the tube inner center line. The probe disk is situatednormal to the axis of the deflection magnet 130. The metal disk isbiased to −18 V to collect positive ions. Other disk bias levels couldalso be used. If the deflection magnet coil current is zero, then verylittle ion current arrives at the probe disk. This is shown in FIG. 5.The average DC ion current collected at the probe disk is shown as thelower curve without any bias voltage applied to the deflector plates140, 142. The upper curve with higher ion current is for the respectivemagnetic field of the deflection coil and with the second inner plate142 biased 38V with respect to the first plate 140 at the outer radiusof the bend. The difference in these two curves illustrates the increasein the ion current collected due to the addition of the first and secondelectrostatic deflector plates 140, 142.

It should be noted that the bias voltage applied to the electrostaticdeflector plates 140, 142 can be modulated or changed in value toeffectively paint a region of the substrate 40. Such a modulatedpainting action can be used to make a more uniform thickness film over acertain region of the substrate or to preferentially pattern the depositonto the substrate 40. The electrostatic deflector plates 140, 142 havevery little capacitance so that the voltage could be modulated at a highrate. In contrast to this the magnetic coils have an appreciableinductance which would limit the rate at which the magnetic field valueof the deflection coil could be modulated.

FIG. 6 illustrates a magnetic field pulsed laser deposition system 200according to a third embodiment of the present invention. The system 200includes the target 30, the substrate 40 and a deflection magnet 210.The deflection magnet 210 is generally an annular magnetic member andhas a first end 212 and an opposing second end 214. The deflectionmagnet 210 preferably is formed of an electromagnetic core, i.e., metal,with magnet wire, i.e., #18 gauge copper wire, being wound around thecore. The deflection magnet 210 has an opening 216 extendingtherethrough from the first end 212 to the second end 214. In oneexemplary embodiment, the diameter of the opening 216 is about 3.5 cm.The deflection magnet 210 is preferably a linear member and in contrastto the deflection magnet 130 of FIG. 2, the deflection magnet 210 doesnot have any bend incorporated therein. Thus, the generated plume 31follows a generally linear path through the opening 216 from the target30 to the substrate 40.

In this embodiment, the deflection magnet 210 has an access port 220formed therein at a selected location near the first end 212. The target30 is coupled to a rotatable target holder 29. The dimensions of thetarget 30 and the target holder 29 are such that each is received withinthe opening 216. Typically, the target 30 and the target holder 29 areinserted into the opening 216 at the first end 214 so that the target 30is positioned proximate to the access port 220. The access port 220permits the laser beam from the external laser 20 to pass through theaccess port 220 and strike the rotating target 30 disposed within theopening 216 of the deflection magnet 210.

Similar to the other embodiment, the target 30 is ablated by the laserbeam to generate the plume 31 and the deflection magnet 210 generates amagnetic field axially along the length of the deflection magnet 210.The magnetic field generates an intense plasma (plume 31) and magnetizesthe electrons and causes them to spiral along the longitudinal axis ofthe deflection magnet 210 resulting from the laser pulse. The magneticfield magnetizes the electrons causes them to spiral along the magneticfield lines with a generally helical radius that is less than thediameter of the opening 216. Because the magnetic field is parallel tothe laser plume, the plume 31 travels through the deflection magnet 210toward the second end 214 where the plume components exit the deflectionmagnet 210 and are deposited onto the substrate 40.

This embodiment does not include the confinement magnet 110 (FIG. 2) asit is not needed due to the target 30 already being disposed within thedeflection magnet 210. In addition, because the deflection magnet 210does not include a bend, the first and second plates 140, 142 (FIG. 3)are not used in this configuration.

The embodiment shown in FIG. 6 is preferably intended for use inapplications where the generation of a high kinetic energy isadvantageous and also because of the substantially linear nature of thedeflection magnet 210, this embodiment should be used for applicationshaving pure or highly pure targets 30. Because the atomic clusters andany particulates formed during the laser ablation process follow a pathalong the magnetic field lines within the opening 216, these componentsare also directed at the substrate 40. The substrate 40 is disposed nearthe second end 214 and is spaced in an axial relationship with theopening 216 so that the plume 31 is deposited directly onto thesubstrate 40. In applications where the target is sufficiently pure,i.e. carbon applications, this embodiment may be used as theseapplications typically do not produce a significant amount of atomicclusters and particulates, both of which are undesirable.

FIG. 7 illustrates a magnetic field pulsed laser deposition system 300according to a fourth embodiment of the present invention. The system300 includes the target 30, the substrate 40 and a deflection magnet310. The deflection magnet 310 has an “S” shaped configuration andincludes a first end 312 and an opposing second end 314. The deflectionmagnet 310 is preferably a substantially annular member and is formed ofan electromagnetic core, i.e., metal, with magnet wire, i.e., #18 gaugecopper wire, being wound around the core. The deflection magnet 310 hasan opening 316 extending therethrough from the first end 312 to thesecond end 314. In one exemplary embodiment, the diameter of the opening316 is about 3.5 cm. In this embodiment, the deflection magnet 310 hasan access port 320 formed therein at a selected location near the firstend 312. The target 30 is coupled to the rotatable target holder 29 andboth are inserted into the opening 316 at the first end 314 so that thetarget 30 is positioned proximate to the access port 320.

According to this embodiment, the deflection magnet 310 has two bendsdesigned into its structure. More specifically, the deflection magnet310 has a first bend 330 and a second bend 340. The first bend 330 isformed between the first end 312 and the second end 314, while thesecond bend 340 is formed at the second end 314. Preferably, each of thefirst and second bends 330, 340 has a 45° angle and therefore incombination, the first and second bends 330, 340 produce an “S” shapedconfiguration for the deflection magnet 310.

The deflection magnet 310 preferably includes two sets of first andsecond deflector plates 140, 142 and plates 144, 146 with the first andsecond plates 140, 142 being associated with the first bend 330 and thefirst and second plates 144, 146 being associated with the second bend340. As shown in the cross-sectional view of FIG. 7, there is a section311 of the deflection magnet 310 which intersects the initial axialdirection of travel of the plume 31 and therefore, the plume 31 willstrike the section 311 if the plume 31 traveled in a linear directionafter it is formed in the opening 316. As with the embodiment of FIG. 2,the plate 140 disposed along the first section 311 is charged negativelyso as to repel the negative electrons and cause the electrons to travelaround the first bend 330. The first plate 144 is charged negativelywith respect to the second plate 146 to assist the electrons intraveling around the second bend 340. In other words, the plates 140,142 and the plates 144, 146 exert an electrical field that prevents theelectrons from moving to the outside bend radius and away from thedirected plume 31. The electric field directed across the opening 316from the second plate 146 to the first plate 144 disposed along thesecond bend 340 of the deflection magnet 310 helps keep the negativeelectrons away from the curvature 313 of the second bend 340. The ionsare attracted to the electrons and are thus assisted to follow theelectrons along the magnetic field direction and the ions successfullynavigate the first 45° bend 330 and then the second reverse 45° bend340.

The substrate 40 is disposed proximate to and in axial relationship withthe opening 316 so that the plume 31 is deposited onto the substrate 40after negotiating the second bend 340. Because the first bend 330preferably is a 45° bend and the second bend 340 is a 45° bend, theplume 31 exits parallel to the initial plume direction after it has beenformed and travels within the opening 316 before encountering the firstbend 330. As with the embodiment of FIG. 2, the incorporation of thefirst and second bends 330, 340 is designed to filter the undesiredmaterial from the plume 31 because the uncharged matter is notinfluenced by the magnetic field and travels in a linear-direction fromits formation. In other words, the atomic clusters and the largeparticulates do not effectively navigate the first and second bends 330,340.

This embodiment has several advantages. First, the basic geometry of adeposition chamber can be retained with a lateral displacement of thetarget holder 29 being the principle geometry change required. Second,better particulate filtering is achieved due to the additional bendingintroduced by the second bend 340. Third, the ions that tend to drift tothe outside of the first bend 330 are then on the inside of the bend forthe second bend 340.

FIG. 8 illustrates a magnetic field pulsed laser deposition system 400according to a fourth embodiment of the present invention. The system400 includes the target 30, the substrate 40, the confinement magnet 110and the deflection magnet 210. The fourth embodiment is similar to thesecond embodiment in that the plume 31 is passed through the confinementmagnet 110 before it enters the deflection magnet 210. One of the maindifferences between the second and fourth embodiments is that the accessport 220 is eliminated in the fourth embodiment. Instead, the target 30and the target holder 31 are positioned outside of the deflection magnet210 as in the second embodiment. By eliminating the need for the laseraccess port 220, stronger magnetic fields can be generated withoutexcessive heating considerations as arise when a resistive coil is used.By eliminating the access port 220, additional current may be driventhrough the deflection magnet 210.

As in the second embodiment, the plume 31 is focused by the magneticfield of the confinement magnet 110 before it is directed into thedeflection magnet 210 which is a linear member. The parallel magneticfield generated by the deflection magnet 210 causes the electrons tospiral along the magnetic field lines with a generally helical radiusand the ions are “dragged” by the electrons to the substrate. By usingthe confinement magnet 110 to focus the plume 31, the magnetic field ofthe deflection magnet 210 does not have to be as strong in order tostart directing the electrons through the deflection magnet 210.

As previously-mentioned in the discussion of the second embodiment, thisarrangement is more suited for applications where the target 30 is pureor has a high level of purity since the linear nature of the deflectionmagnet 210 causes all of the components of the plume 31 to be directedat the substrate 40.

FIG. 9 illustrates a magnetic field pulsed laser deposition system 500according to a fifth embodiment of the present invention. The system 500is similar to the system 300 of the third embodiment with the exceptionbeing that the target 30 and target holder 31 are disposed outside ofthe deflection magnet 310. Instead, the confinement magnet 110 is usedto focus and converge the plume 31 after it is formed by directing thelaser beam onto the target 30. The plume 31 then passes into the opening316 of the deflection magnet 310 where it is influenced by the magneticfield as previously discussed with reference to FIG. 7. Because of the“S” shaped configuration of the deflection magnet 310, the plume 31 iseffectively filtered so that only the desired components, i.e., theatomic species atoms and ions, are directed onto the substrate 40 toform the thin film. This permits any number of target materials to beused without substantial concern as to the purity of the target.

Each of the systems of the various embodiments of the present inventionare preferably performed in a vacuum environment, such as a vacuumchamber. In addition, the substrate 40 is often cleaned prior to beingused in the system. Conventional substrate cleaning techniques may beused, including using several ultrasonications in heptane, followed by adrying in a stream of dry nitrogen gas. Prior to loading the substrate40 into the vacuum chamber, any organic residue or other contaminationon the substrate surface is preferably removed using laser ablationusing the same excimer laser which is used to produce the thin film. Thesubstrate 40 may be maintained at room temperature and can be heated, ifnecessary, to improve film adhesion and/or crystallinity. The substrate40 may also be biased, floated, or held at ground potential.

Now referring to FIG. 10 in which another exemplary embodiment is shownin the form of an ion assisted pulsed laser deposition system 600. Thesystem 600 has some similar components as the other previously describedsystems and therefore, for sake of brevity, similar or alike componentswill be not described in great detail. The system 600 includes excimerlaser 20 and in one embodiment, the laser light preferably has anultraviolet wavelength of about 248 nm and operates at approximately1-1.3 J per pulse. As with the other systems, the system 600 and amethod of operation thereof produce thin particulate free diamond likecarbon films that can be made with good adhesion onto even roomtemperature substrates. The present method, as described below, employsa filtered ionized carbon beam created by the vacuum impact of the laser20 onto the target 30. The resultant deposition beam can be steered anddeflected by magnetic and electric fields to paint a specific surface ofsubstrate 40. It is also within the scope of the present system 600 thatthe substrate 40 can be heated by heater 41 to and elevated temperature.

One advantage of this deposition method is that the resultant films areparticulate free and formed only as the result of atomic species impact.The carbon films exhibit the high hardness characteristic of diamondlike carbon (DLC) films. It should be noted that particulate free filmscan be deposited by this method that are either metallic,semi-conducting, or insulating.

The system 600 also includes the confinement magnet 110 formed of thepair of permanent magnets 112, 114 which are used to produce a magneticfield parallel to the plume ejection direction in front of the lasertarget 30. Each of the magnets 112, 114 has a north (N) pole 116 and asouth (S) pole 118. Magnets 112, 114 are arranged so that the N pole 116of the magnet 112 opposes the N pole 116 of the magnet 114 and the Spole 118 of the magnet 112 opposes the S pole 118 of the magnet 114. Thelike magnetic poles 116, 118 oppose each other so that the magneticfield from each of the magnets 112, 114 loops from the N magnetic pole116 to the S magnetic pole 118 of each of magnets 112, 114 creating amagnetic field that is substantially parallel to the plume direction.This parallel magnetic field prevents the plume 31 from furtherconverging and actually causes the plume 31 to become refocused into anarrow plume 31 as it travels through the confinement magnet 110.

In one embodiment, the confinement magnet 110 generates a relativelystrong magnetic field that can be created without introducing a jouleheating that would accompany a magnetic field generated by introducing acurrent in a resistive solenoid. In one embodiment, the target 30 isactually in the form of a plurality of computer selectable targets 30arranged in a predetermined pattern. For example and according to oneexemplary embodiment, there are six targets 30 that are arranged about60 degrees from each other about a ring holder. Each target 30 isrotated about an axis perpendicular to the ring and the ring position isoscillated during deposition so that the laser beam impacts over most ofthe approximately 2.5 cm diameter of the selected target. The surface ofeach target holder 30 is preferably beveled at about 15 degrees awayfrom the ring plane so that the laser beam which is usually directed at45 degrees to the plane of the ring, impacts the target surface atvarying angles from approximately 30 degrees to 60 degrees as the target30 rotates. The beveled nature of the target 30 is indicated byreference number 31 and this beveled target surface thus prevents thelaser beam from forming a constant angle etch pit pattern into thetarget surface that normally slows the laser ablation process once thisconstant angle etch pit pattern becomes established. Since the impactplume is nominally directed normal to target surface, the beveled targetsurface 31 also causes the plume direction to sweep over an arc and morefully randomize the ion spatial distribution that enters the collectormagnet stage (the confinement magnet 110) and the parts downstreamtherefrom. A more even film coating thus also results over the substratesurface. The target erosion continues over a long period of time sincethe target surface does not develop a constant angle etch pit patternthat generally slows the deposition process.

As can be seen from FIG. 10, the gap 117 is formed between the magnets112, 114 and the laser 20 may be positioned so that the laser beam isdirected through this gap 117 onto the target 30. One of the targets 30is disposed a predetermined distance from one end 115 of the magnets112, 114. The distance the selected target 30 should be placed from themagnets 112, 114 depends upon several factors, including but not limitedto the type of material forming the target 30. In any event, the target30 and the magnets 112, 114 should be placed at a distance wheresubstantially all of the plume 31 will be directed into the gap 117. Asbest show in FIG. 10, the central region of the selected target 30 atwhich the laser beam is directed should be axially aligned with the gap117 so that the plume 31 travels into the gap 117.

The system 600 also includes a pulsed coil 610 that is disposedproximate one end of the magnets 112, 114. In the exemplary embodimentthat is illustrated, the coil 610 is a tapered throat high field pulsedcoil that collects the ion beam over a relatively wide solid angle andconcentrates the beam toward the substrate 40. The pulsed coil 610 has afirst end 612 that is proximate one end of the magnets 112, 114 wherethe ion beam exits and an opposing second end 614 that faces thesubstrate 40. The pulsed coil 610 includes a through bore 616 which isaxially aligned with the gap 117 so that the ion beam (plume 31) canexit the confinement magnet 110 (collector stage) and be directed intothe through bore 616 at the first end 612. The pulsed coil 610 isconstructed so that the through bore 616 is of a tapered construction inthat the bore 616 has a greater diameter at the first end 612 and a lessdiameter at the second end 616. In other words, the through bore 616tapers inwardly toward the second end 614.

The laser 20 is triggered only when the current in the pulsed coil 610reached a predetermined threshold value, e.g., about 200 A. The currentin the pulsed coil 610 has a rise time of 1-2 ms to 200-240 A afterwhich the laser 20 is triggered by a comparator circuit. The laser inuse can be triggered at a repetition rate up to 50 Hz. One element thatis not illustrated but is preferably included in the system 600 is awindow protector circuit that prevents atoms from the laser plume 31from coating the inside of the laser entry window. This allows long termdepositions to be done under vacuum conditions so that long mean freepaths are realized for the ion beam.

The system 600 further includes deflector plates 620 that can be used tosweep the ion beam across the substrate 40. In the illustratedembodiment, the deflector plates 620 each includes a planar surface(e.g., they are elongated, planar plates) and they are disposedproximate the second end 614 of the pulsed coil 610. The deflectorplates 620 are orientated and spaced apart from one another such thatthe distance between the plates 620 is about equal to or greater thanthe diameter of the through bore 616 at the second end 614. This permitsthe ion beam that exits the second end 614 of the pulsed coil 610 toenter the space between the deflector plates 620.

Further, a movable mask 630 can optionally be used to pattern thedeposition. The mask 630 has a predetermined pattern formed therein andis disposed between the deflector plates 620 and the substrate 40.

The present deposition system 600 has similarities and differences fromother previous ion deflector systems. One is that for metal elemental oralloy targets, such as Co and Py, a straight through coil can be usedsince particulates are much less of a problem in that case. The actionthen is to produce an ion pulsed modified deposition that allows highfilm adhesion to be obtained onto even room temperature substrates 40.If desired, the pulsed coil 610 can be of the type that includes a 45degree bend which can be substituted to avoid any direct line of sightbetween the target 30 and the substrate 40. Other principle differencesincludes the use of a high field permanent magnet collector stage 110that provides easy access for the laser beam 20 to the six computerselectable targets 30.

There are a number of advantages that are achieved with the presentsystem 600 as compared to conventional sputtering systems including butnot limited to the following. First, the high pulsed ion energy allowsfilms with good adhesion to be deposited onto even room temperaturesubstrates 40. For example, Co films deposited onto room temperatureglass substrates 40 can be forcefully rubbed with a pencil eraserwithout signs of any film degradation.

Conventional sputtered films generally have poor substrate adhesionunless substrate heating is added. If desired, the substrates in thision beam assisted system 600 can be heated during deposition to obtaindirectly deposited crystalline films. The second, is the diamond likecarbon (DLC) type films can be made that are not produced by aconventional sputtering system. The third is the ease with which layeredstructures employing DLC films in conjunction with other magnetic andnonmagnetic layers can be made as the device structures in the samesystem. In one embodiment, a 4.5 cm diameter region is relativelyuniformly coated at a distance of 3 cm beyond the pulsed coil 610. An ACvoltage is applied to the deflector plates 620 of FIG. 10 can be used toobtain greater film thickness uniformity over such a region. A largersystem or substrate motion can be employed to coat larger area wafers.

In one exemplary embodiment, the system 600 with the tapered pulsed coil610 design and utilizing a straight coil, the deposition enhancementfactor has been measured by comparing the optical transmission of filmsdeposited with the permanent magnet section 110 and the pulsed coilcurrent to films deposited in the same geometry without the permanentmagnet section 110 and without coil current pulsing. Cobalt filmsdeposited for the same number of laser pulses with the permanent magnetsection 110 and coil pulsing measured an optical density of 3.0. Whencobalt films were deposited without the permanent magnet section 110 andwithout coil current, an optical density for the films of 0.20 wasobtained. (Optical density is defined as log₁₀(I₀/I_(t)). An opticaldensity of 3 means that only 1 part in 1000 or 0.1% of the incidentlight is transmitted. An optical density of 0.20 means that 63% of theincident light is transmitted.

In another aspect of the present invention and as illustrated in FIG.11, a device 700 is provided to overcome the following problem. In apulsed laser deposition system, a high energy defocused laser beamenters a deposition system through a window to ablate material from alaser target 30. Part of the generated plume of material 31 is thencollected onto a substrate to form a film but a part of the plume 31 cantravel back along the line of sight of the laser beam to coat the insideof the laser entry window and then impede further entry of the laserbeam into the system. Normally, a low pressure inert gas, such as argon,is used inside the chamber to slow the coating of the inside of thelaser entry window. But when depositions requiring a relatively longmeans free path for the plume 31 is required, as in any system requiringion collection and deflection, the gas protecting the window alsoimpedes the ion beam. The device 700 addresses this problem and allowslong term depositions under vacuum conditions to become possible.

The device 700 acts to keep the inside of the deposition chamber entrywindow from being coated by the laser pulse generated plume 31 of atoms,ions, and particles released from the laser target 30. The device 700includes a pair of metal plates 710 and a pair of radioactive plates 720that are arranged relative thereto with both being proximate the lasertarget 30. Each plate 710 has a first end 712 and a second end 714 andthe radioactive plate 720 has a first end 722 and a second end 724 withthe first ends 712, 724 being preferably aligned with one another. Themetal plates 710 are spaced apart from one another so that a space 716is formed therebetween which can accommodate the radioactive plates 720and still leave a space between the radioactive plates 720 to permit thelaser beam to travel from one end 714 of the plates 710 to the other end712 of the plates 710. In one exemplary embodiment, each metal plate 710measures approximately 16 cm long by 6 cm depth into the plane as shownin FIG. 11. The radioactive coated plates 720 measure 8 cm in length by6 cm depth into the plane of the FIG. 11. In this embodiment, theradioactive plates 720 are attached to the back section of the metalplates 710. Thus, the length of the radioactive coated plate 720 isequal to or approximately ½ the length of the metal plates 710.

As illustrated, a plurality of posts 730 (e.g., ceramic posts) aredisposed between the metal plates 710 in the area from the ends 724 ofthe radioactive plates 720 to the ends 714 of the metal plates 710. Inone embodiment, the posts 730 separate the metal plates 710 by about 3cm. The posts 730 provide structural support to the components as wellas spacing the plates 710 apart. A potential difference (e.g., a 1500volt potential difference) is applied between the metal plates 710. Asillustrated in FIG. 11, one of the metal plates 710 can be at groundpotential for ease in attaching the structure near the vacuum side of alaser entry window, generally indicated at 740.

The device 700 acts to keep the inside of the deposition chamber laserentry window 740 from being coated by the laser pulse generated plume ofatoms, ions and particles released from the laser target 30. The ingeneral converging pulsed laser beam enters the deposition through thelaser entry window 740 while being focused to impinge upon the lasertarget 30. In general, the laser beam must still be defocused whileentering the chamber to avoid damaging the laser entry window 740. Thespacing between the metal plates 710, radioactive plates 720, andinsulating posts 730 is made large enough so as not to interfere withthe converging laser from reaching the target 30. After the focusedlaser beam impacts the laser target 30, a plume 31 of atoms, ions andparticulates is generated. Part of this generated plume of ions is thencaptured and focused by the magnet 110 and deflector coils to coat thesubstrates 40 with the desired materials. But part of the plume ofmaterial is also emitted in a direction back along the site of the laserbeam which would soon coat the inside of the laser window 740 with acoating of material that then interferes with the subsequent entry ofthe laser pulses into the chamber.

In a conventional pulse laser deposition system, a low pressure of gas,such as argon, is maintained inside the deposition system so that theplume 31 is directed back toward the laser entry window 740 and isscattered by gas atom collisions to help keep the inside of the laserentry window 740 clean. The laser entry window 740 must usually becleaned frequently often after only one or two deposition runs. In mostpractical PLD systems, the distance from the inside of the laser entrywindow 740 to the laser target 30 is made greater than the distance fromthe laser target 30 to the substrate 40 on to which the deposition iscollected. But this gas used to help keep the inside of the laser entrywindow 740 clean also acts to scatter the plume of ions and any ionssubsequently deflected and used to facilitate a film deposition. Ifattempts to operate the pulsed laser deposition system under vacuumconditions to facilitate a long mean free path for ion deposition plumethen the inside of the laser entry window 740 may become sufficientlycoated so as to restrict subsequent laser pulse entry into the systemafter only a few minutes of operation. Further deposition could thenonly be possible after stopping to clean the inside of the laser entrywindow 740.

The system 700 solves this problem by allowing continued long termdeposition under vacuum conditions without the inside of the laser entrywindow 740 becoming coated. The action is such that the plume of atoms,ions and particulates, heading back toward the entry window 740, isionized by the stream of radioactive alpha particles, beta particles,and gamma rays released from the radioactive plates 720. The ionizedplume material is then deflected toward one of the metal plates 710 andthus no longer coats the inside of the laser entry window 740. Inoperation, the pulsed laser deposition system 700 may then be operatedunder vacuum conditions for weeks at a time before it then becomesnecessary to clean the inside of the laser entry window 740.

The radioactive plates 720 can come from any number of differentsources. For example, the radioactive plates 720 can be coated with aglaze of made from uranium salt trailings. Any other radioactive sourceof the proper activity can be used. Only microcuries or less ofactivity, which is below licensing requirements, is required.

Using the PLD method of the present invention, extremely clean anduniform coatings formed from a number of single element targets as wellas multi-element targets may be produced. For example, cobalt, permalloy(Ni, Fe based alloys), samarium cobalt, titanium carbide and nitride andcarbon and diamond-like carbon films, to name a few, may be formed usingthe PLD method of the present invention. The present method allows filmsto be deposited onto bare substrates as well as onto previously madefilm layers including metallic, glassy or amorphous materials,insulating and semiconductor materials.

Further, using the present PLD method, diamond-like carbon films havebeen deposited onto glass and other types of substrates, such as an Sisubstrate. The present films can be deposited onto metallic, glass,insulating and semiconductor substrates. A particularly useful potentialapplication involves the deposition of diamond-like carbon films as apart of semiconductor magnetic tunnel junctions. The magnetic field PLDsystems of the present invention demonstrate particulate reductionwithout sacrificing film growth rates. Furthermore, the presentinvention also offers additional advantages relative to otherconventional systems. For example, the PLD method of the presentinvention permits the removal of the atomic clusters and particulatesfrom the atomic species contained in the plume without the introductionof physical shadowing that requires the introduction of sufficient gaspressure to physically scatter the atomic species behind the shadow. Therelative surface mobility of the directed plume atoms arriving at thesubstrate 40 can be controlled by controlling the pulse repetition rate.Also, since the transit time to the substrate 40 can be short comparedto the time between pulses, the deflection and confinement magnets canbe operated in a pulsed mode also to minimize the total power dissipatedby these electromagnets.

Accordingly, the present invention, provides a simple, relativelyinexpensive, yet effective PLD method of forming extremely clean filmswith reduced particulate densities and size. This method favors usefulfilm properties, such as crystallinity and good adhesion, event at roomtemperature, because it relies upon using high energy ions for thedeposition. The method therefore has tremendous potential forapplications where the substrate is thermally sensitive. The presentmethod may be applied to the production of a film from a great number ofmaterials.

Several attributes of the present invention, such as the incorporationof a laser entry window stay clean circuit, and the use of beveled facedrotating targets, allow repeated long term depositions to be made inrapid succession.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A device for maintaining cleanliness of aninterior of a deposition chamber laser entry window through which alaser beam enters and converges to a target, the device comprising: alaser entry window; a laser ablation target that is positioned relativeto said laser entry window such that the target can be ablated by alaser beam entering the deposition chamber through said laser entrywindow; a pair of first members disposed between the laser entry windowand the target, the first members being spaced a distance apart from oneanother; a pair of radioactive members disposed in the space between thepair of first members; and wherein the first members are operativelyconnected to a voltage source and ground so that a voltage potentialdifference is created therebetween, the converging laser beam enteringthe space between the first members at one end thereof and travelingtherebetween in a converging manner toward the target and wherein aplume that is generated when the laser beam ablates the target isionized by the radioactivity of the radioactive members such that theionized plume is deflected toward one of the first members as opposed tocoating the interior of the laser entry window.
 2. The device of claim1, wherein each of the first members comprises a conductive plate, oneof the conductive plates being connected to the voltage source, theother being connected to ground.
 3. The device of claim 1, wherein eachof the radioactive members comprises a radioactive plate.
 4. The deviceof claim 3, wherein the radioactive plates are attached to backsides ofthe first members which are in the form of metal plates.
 5. The deviceof claim 4, wherein first ends of the radioactive plates align withfirst ends of the metal plates and each radioactive plate has a lengthless than a length of the metal plate.
 6. The device of claim 5, whereinthe length of each radioactive plate is about ½ the length of the metalplate.
 7. The device of claim 1, further including a plurality ofinsulating posts disposed between the first members at locations whichare free of the radioactive members.
 8. The device of claim 7, whereinthe insulating posts space the metal plates apart by about 3 cm.
 9. Amethod for maintaining cleanliness of an interior of a depositionchamber laser entry window through which a laser beam enters andconverges to a target, the method including the steps of: disposing apair of first members between the laser entry window and the target, thefirst members being spaced a distance apart from one another; disposinga pair of radioactive members in a space between the pair of firstmembers; operatively connecting the first members to a voltage sourceand ground, respectively, so that a voltage potential difference iscreated therebetween; ablating the target with a laser beam creating aplume; and ionizing components of the plume by the radioactivity of theradioactive members thereon such that the ionized plume is deflectedtoward one of the first members as opposed to coating the interior ofthe laser entry window.
 10. The method of claim 9, wherein the voltagepotential difference is about 1500 V.
 11. The method of claim 9, whereineach of the first members comprises a conductive plate, one of theconductive plates being connected to the voltage source, the other beingconnected to ground, each of the radioactive members comprising aradioactive plate that is attached to one backside of one first member.12. The method of claim 11, further including the step of: aligningfirst ends of the radioactive plates with first ends of the metalplates, wherein each radioactive plate has a length less than a lengthof the metal plate.
 13. The method of claim 9, further including thestep of: disposing a plurality of insulating posts between the firstmembers at locations which are free of the radioactive members.